scholarly journals On the multipath effects due to wall reflections for wave reception in a corner

Noise Mapping ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 41-64
Author(s):  
Luiz Manuel Braga da Costa Campos ◽  
Manuel José dos Santos Silva ◽  
Agostinho Rui Alves da Fonseca
Keyword(s):  
Electromagnetic Waves ◽  
Double Series ◽  
Two Dimensions ◽  
Reflection Coefficients ◽  
Urban Air ◽  
Interference Effects ◽  
Direct Signal ◽  
Total Signal ◽  
Spectral Bands ◽  
Multipath Effects

Abstract Multipath effects occur when receiving a wave near a corner, for example, the noise of an helicopter or an aircraft or a drone or other forms of urban air mobility near a building, or a telecommunications receiver antenna near an obstacle. The total signal received in a corner consists of four parts: (i) a direct signal from source to observer; (ii) a second signal reflected on the ground; (iii) a third signal reflected on the wall; (iv) a fourth signal reflected from both wall and ground. The problem is solved in two-dimensions to specify the total signal, whose ratio to the direct signal specifies the multipath factor. The amplitude and phase of the multipath factor are plotted as functions of the frequency over the audible range, for various relative positions of observer and source, and for several combinations of the reflection coefficients of the ground and wall. It is shown that the received signal consists of a double series of spectral bands, in other words: (i) the interference effects lead to spectral bands with peaks and zeros; (ii) the successive peaks also go through zeros and “peaks of the peaks”. The results apply not only to sound, but also to other waves, e.g., electromagnetic waves using the corresponding frequency band and reflection factors.

Manufacturing Metamaterials Using Synchrotron Lithography

2010 ◽  
Vol 75 ◽  
pp. 230-239
Author(s):  
Herbert O. Moser ◽  
Linke Jian ◽  
Shenbaga M.P. Kalaiselvi ◽  
Selven Virasawmy ◽  
Sivakumar M. Maniam ◽  
...  
Keyword(s):  
Electromagnetic Waves ◽  
Cost Effective ◽  
Pattern Generation ◽  
Geometrical Parameters ◽  
X Ray ◽  
Spectral Bands ◽  
Left Handed ◽  
Aspect Ratios ◽  
Multi Level ◽  
Primary Pattern

The function of metamaterials relies on their resonant response to electromagnetic waves in characteristic spectral bands. To make metamaterials homogeneous, the size of the basic resonant element should be less than 10% of the wavelength. For the THz range up to the visible, structure details of 50 nm to 30 μm are required as are high aspect ratios, tall heights, and large areas. For such specifications, lithography, in particular, synchrotron radiation deep X-ray lithography, is the method of choice. X-ray masks are made via primary pattern generation by means of electron or laser writing. Several different X-ray masks and accurate mask-substrate alignment are necessary for architectures requiring multi-level lithography. Lithography is commonly followed by electroplating of metallic replica. The process can also yield mould inserts for cost-effective manufacture by plastic moulding. We made metamaterials based on rod-split-rings, split-cylinders, S-string bi-layer chips, and S-string meta-foils. Left-handed resonance bands range from 2.4 to 216 THz. Latest is the all-metal self-supported flexible meta-foil with pass-bands of 45% up to 70% transmission at 3.4 to 4.5 THz depending on geometrical parameters.

scholarly journals Взаимодействие электромагнитной H-волны с тонкой металлической пленкой на диэлектрической подложке в случае анизотропной поверхности Ферми металла

2019 ◽  
Vol 127 (8) ◽  
pp. 306
Author(s):  
И.А. Кузнецова ◽  
Д.Н. Романов ◽  
А.А. Юшканов
Keyword(s):  
Fermi Surface ◽  
Effective Mass ◽  
Free Path ◽  
Electromagnetic Waves ◽  
Metal Film ◽  
Mean Free Path ◽  
Thin Metal Film ◽  
Thin Metal ◽  
Reflection Coefficients ◽  
Conduction Electrons

The interaction of electromagnetic H-waves with the thin metal film subject to the shape of the ellipsoidal Fermi surface and a constant mean free path of electrons for various angles of incidence of the electromagnetic waves of theta and different from each other of the coefficients of specularity of q1 and q2 in the reflection of electrons from surfaces of the film is calculated. The metal film is enclosed between two media with permittivity ε1 and ε2. The behavior of reflection coefficients R, passage T and absorption A from the effective mass of conduction electrons is analyzed.

scholarly journals Causes and nature of ice-sheet radio-echo internal reflections estimated from the dielectric properties of ice

1994 ◽  
Vol 20 ◽  
pp. 80-86 ◽  
Author(s):  
Shuji Fujita ◽  
Shinji Mae
Keyword(s):  
Dielectric Properties ◽  
Crystal Orientation ◽  
Electromagnetic Waves ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Volcanic Eruptions ◽  
Microwave Frequency ◽  
Reflection Coefficients ◽  
Single Plane ◽  
Deep Layers

The causes and nature of ice-sheet radio-echo internal reflections at deep layers in polar ice sheets are discussed, based on the dielectric properties of ice that have been measured at microwave frequency and radio frequency. The reflection coefficients of electromagnetic waves in ice sheets due to two causes the change in permittivity induced by changes in crystal-orientation fabrics with depth, and changes in conductivity induced by changes in acidity with depth - were derived respectively as a function of the frequency used in radar sounding and the temperature of ice, and both were compared quantitatively. It is shown that at single-plane boundaries the reflection coefficients due to the former cause are independent of frequency and temperature and that they are large enough to produce dominant internal reflections. In contrast, reflection coefficients due to the latter cause strongly depend on frequency and temperature. Since they are inversely proportional to the frequency, the latter cause can be dominant only when frequencies below about 60 MHz are used. Examination of previous observational data has suggested that not only changes in acidity but also changes in crystal-orientation fabrics exist at depths corresponding to the dates of earlier volcanic eruptions.

scholarly journals Causes and nature of ice-sheet radio-echo internal reflections estimated from the dielectric properties of ice

1994 ◽  
Vol 20 ◽  
pp. 80-86 ◽  
Author(s):  
Shuji Fujita ◽  
Shinji Mae
Keyword(s):  
Dielectric Properties ◽  
Crystal Orientation ◽  
Electromagnetic Waves ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Volcanic Eruptions ◽  
Microwave Frequency ◽  
Reflection Coefficients ◽  
Single Plane ◽  
Deep Layers

The causes and nature of ice-sheet radio-echo internal reflections at deep layers in polar ice sheets are discussed, based on the dielectric properties of ice that have been measured at microwave frequency and radio frequency. The reflection coefficients of electromagnetic waves in ice sheets due to two causes the change in permittivity induced by changes in crystal-orientation fabrics with depth, and changes in conductivity induced by changes in acidity with depth - were derived respectively as a function of the frequency used in radar sounding and the temperature of ice, and both were compared quantitatively. It is shown that at single-plane boundaries the reflection coefficients due to the former cause are independent of frequency and temperature and that they are large enough to produce dominant internal reflections. In contrast, reflection coefficients due to the latter cause strongly depend on frequency and temperature. Since they are inversely proportional to the frequency, the latter cause can be dominant only when frequencies below about 60 MHz are used. Examination of previous observational data has suggested that not only changes in acidity but also changes in crystal-orientation fabrics exist at depths corresponding to the dates of earlier volcanic eruptions.

The Structural Design Method of Multi-Layer Parabolic Reflective Surface for X-Ray Focusing

2013 ◽  
Vol 552 ◽  
pp. 75-78
Author(s):  
Miang Zhao Ouyang ◽  
Yue Gang Fu ◽  
Zhi Ying Liu ◽  
Jia Ke Wang ◽  
Wen Jun He
Keyword(s):  
Structural Design ◽  
Electromagnetic Waves ◽  
Critical Angle ◽  
Design Method ◽  
Grazing Incidence ◽  
High Energy ◽  
Entrance Pupil ◽  
X Ray ◽  
Spectral Bands ◽  
Effective Aperture

As an ultra-short electromagnetic waves, X-ray has a strong ability to penetrate with high-energy. The method for focusing visible spectral bands is not suitable for X-ray spectrum. At present, in X-ray astronomy, the X-ray focus mode which uses grazing incidence less than critical angle has been widely used. However, the small critical angle limits its effective aperture of the X-ray collection. This paper presents a multi-layer reflective structure working with grazing incidence and the surfaces coated multilayer high reflective for X-ray. It can guarantee the large effective entrance pupil and high energy collection. The 200mm diameter X-ray focusing device is designed as an example. It is found from simulation that a good focusing result is acquired.

scholarly journals Diffraction of Electromagnetic Waves

2010 ◽  
Vol 65 (1-2) ◽  
pp. 1-24 ◽  
Author(s):  
Ulrich Brosa
Keyword(s):  
Stationary Phase ◽  
Electromagnetic Waves ◽  
Fresnel Diffraction ◽  
Two Dimensions ◽  
Method Of Stationary Phase ◽  
General Method ◽  
Explicit Expressions

AbstractThe general method to obtain solutions of the Maxwellian equations from scalar representatives is developed and applied to the diffraction of electromagnetic waves. Kirchhoff’s integral is modified to provide explicit expressions for these representatives. The respective integrals are then evaluated using the method of stationary phase in two dimensions. Hitherto unknown formulae for the polarization appear as well as for imaging by diffraction. Ready-to-use formulae describing Fresnel diffraction behind a round stop are presented.

Precision measurement of complex reflection coefficients of electromagnetic waves in rectangular waveguides

1991 ◽  
Vol 34 (11) ◽  
pp. 1166-1167
Author(s):  
E. G. Alyab'ev ◽  
O. F. Kiselev ◽  
A. V. Myl'nikov ◽  
V. D. Frumkin ◽  
B. A. Khvorostov ◽  
...  
Keyword(s):  
Precision Measurement ◽  
Electromagnetic Waves ◽  
Reflection Coefficients ◽  
Complex Reflection ◽  
Rectangular Waveguides

scholarly journals Analysis of Bistatic Scattering of Electromagnetic Waves by Melting Layer

2011 ◽  
Vol 1 ◽  
pp. 41-43
Author(s):  
Binay Kumar Jha
Keyword(s):  
Electromagnetic Waves ◽  
Mie Theory ◽  
Propagation Path ◽  
Bistatic Radar ◽  
Interference Effects ◽  
Melting Layer ◽  
Bistatic Scattering ◽  
Rain Rates ◽  
The Impact

In this communication bistatic scattering of electromagnetic waves by the melting layer of precipitation has been presented. The bistatic radar reflectivities have been formulated and can be computed at 1- 100GHz by applying the Mie theory for raindropsize distributions at rain rates below 12.5mm/h. It is very important to study the integrated interference effects all along the propagation path as well as of greatest interest for evaluating the impact of the melting layer effects on bistatic interference for communications.Key words: Bistatic scattering; Interference; Hydrometeors; Melting layerThe Himalayan Physics Vol.1, No.1, May, 2010Page: 41-43Uploaded Date: 28 July, 2011

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